This invention relates to a weather strip for use in an automobile, for example.
The term "weather strips" as used in the present invention means strips of material attached to the edges of such stationary window glasses as a windscreen, a rear window and quarter windows, to the joints of a hood, doors and a sun roof, and to the sliding parts between doors and door glasses in an automobile so as to protect the automobile interior against wind, rain, dust, sound, cold and heat prevailing in the ambience. The weather strips embrace window frame rubber molds (FIG. 1), door weather strips (FIGS. 2 to 6), and glass-run strips.
In the specification, the present invention will be described with reference typically to a door weather strip W1 for a trunk lid which, as illustrated in FIG. 2, comprises a flange retaining part having a U-shaped cross section containing an embedded insert 1 and provided on the interior thereof with nipping lips 3, 3 and a hollow sealing part 7 and a lip sealing part 9 protruding respectively from the top side and one lateral side of the flange retaining part 5. The door weather strips contemplated by this invention are not limited to this particular construction.
These weather strips have been heretofore manufactured generally by a procedure which comprises extrusion molding such a rubber compound as ethylene-propylene rubbers (EPDM or EPM) or chloroprene rubber (CR) into a strip in a shape having a flange retaining part 5 spread out and then injecting a sealant into the bottom part 5a of the flange retaining part 5 while the flange retaining part 5 is being laterally bent in the shape of the letter U (Japanese Patent Laid-open publication SHO No. 59(1984)-140,145). This injection of the sealant is intended to ensure the sealing function of the weather strip.
As the sealant, it has been known to use a water-swelling composition (Japanese Utility Model Laid-open publication SHO No. 62(1987)-68,850) which, for the sake of prevention of rusting, incorporates rustproofing agents disclosed in Japanese Patent Laid-open publication SHO No. 62(1987)-74,984 in combination with highly absorbent polymers.
An attempt at extrusion molding the weather strip integrally with the sealant entails four-color extrusion (solid rubber, sponge rubber, insert, and sealant) and consequently brings about a disadvantage that the extrusion molding device used therefor has a highly intricate construction.
Further, since the sealant mentioned above is formed by having highly absorbent polymers dispersed in a water-swelling composition, it does not necessarily permit rapid diffusion and absorption of water and effects prompt manifestation of the sealing property only with difficulty. Moreover, the water seeping to the bottom part 5a of the groove of the flange retaining part 5 keeps the sheet metal part (leading end of the flange part 21) in a wet state for a long time. It is inferred therefore that the persistence of this wet state offsets the effect expected to be brought about by the rustproofing agents incorporated in the water-swelling composition.
Where the water swelling composition uses as its base polymer such a nonpolar macromolecular substance as EPDM, it is suspected that the composition entail the following drawbacks in addition to the problems mentioned above.
(1) Since the highly absorbent polymers are generally polar macromolecules, it binds weakly to the base polymer which is a nonpolar macromolecule. The sealant, therefore, is liable to be rubbed and worn by the leading end of the flange part when it is exposed to the vibrations and shocks produced by the automobile during its travel, with the result that the highly absorbent polymers and the rustproofing agents as well as the base polymer lose weight and the sealant is heavily deprived of the sealing property and the rustproofing properties with elapse of time.
(2) Since the rustproofing agents are generally a polar compound, it is liable to migrate to the surface of the sealant. The rustproofing agents exuding to the surface of the sealant, on contact with water, flow out at once in a large volume. Thus, the decrease of the rustproofing effects are aggravated with elapse of time.
(3) The water-swelling composition incorporates therein surfactants for the purpose of enhancing the affinity of the base polymer for water (polar compound) and consequently facilitating the permeation of water into the water-swelling composition. Since the surfactants are disposed to flow out on contact with water, however, the water-swelling composition is gradually deprived of its affinity for water and its ability to absorb water to full depth, with the result that the absorbent polymers come to contribute only partially to the function of water absorption. Thus, the capacity of the absorbent polymers for inflation (a phenomenon contributory to the sealing action) is degraded.
(4) As the inflation of the sealant with absorbed water and the contraction thereof by drying are alternated repeatedly, the highly absorbent polymers flow out of the composition and the rustproofing agents are lost intolerably.